The world’s urban population increased from about 200 million (15% of world population) in 1900 to 2.9 billion (50% of world population) in 2000, and the number of cities with populations in excess of 1 million increased from 17 in 1900 to 388 in 2000. As people are increasingly living in cities, and as cities act as both human ecosystem habitats and drivers of ecosystem change, it will become increasingly important to foster urban systems that contribute to human well-being and reduce ecosystem service burdens at all scales

Urbanization is not in itself inherently bad for ecosystems. Many ecosystems in and around urban areas are more biodiverse than rural monocultures are, and they can also provide food, water services, comfort, amenities, cultural values, and so on, particularly if they are well managed. Urban Biodiversity is gaining more and more importance and Urban Rainforests are being created in many cities of the world. Fostering Moreover, urban areas currently only account for about 2.8% of the total land area of Earth, despite containing about half the world’s population.